Auto-focus apparatus, focus adjusting method, image capturing apparatus and image capturing method

ABSTRACT

An auto-focus apparatus, a focus adjusting method, an image capturing apparatus and an image capturing method make it possible to perform accurate focus adjustment on a subject for which the focus should be adjusted. The auto-focus apparatus emits an irradiation wave from emitting means for irradiation to a subject while changing an incident angle of the irradiation wave, detects an incident angle of a reflected wave of the irradiation wave reflected by the subject, incident on light receiving means positioned corresponding to the emitting means, determines based on the emitting angle and the incident angle whether or not the subject is a subject for which the focus is adjusted, and adjusts the focus on the subject when determining that the subject is the subject for which the focus should be adjusted, thereby making it possible to accurately adjust the focus on the subject for which the focus should be adjusted.

This is a continuation of application Ser. No. 09/731,133, filed Dec. 6,2000, now U.S. Pat. No. 6,917,386, the entirety of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an auto-focus apparatus, a focusadjusting method, an image capturing apparatus and an image capturingmethod, and more particularly, is suitably applied, for example, to avideo camera.

2. Description of the Related Art

Conventionally, video cameras contain a so-called auto-focus functionwhich automatically performs a focusing operation of a lens inaccordance with the distance to a subject (subject distance). Forrealizing such an auto-focus function, a variety of focus detectingmethods have been devised for detecting a defocused state, and amongothers, an image processing method, an infrared method and a phasedifference detecting method are representative.

The image processing method picks up a central region from an imagecaptured by an imaging device (CCD: Charge Coupled Device), extractshigh frequency components from the picked-up region, and adds the highfrequency components to generate a value which is used as an evaluationvalue for detecting the focus. This evaluation value becomes higher asan image of a subject being captured approaches a focused state, andbecomes lower as the image is further away from the focused state afterit presents the highest value at the position of the focused state.Therefore, the image processing method moves the focus to examinewhether the evaluation value increases or decreases, and adjusts thefocus while moving the focus in a direction in which the evaluationvalue becomes higher until the focused state is reached. In other words,the image processing method performs a so-called hill climbingoperation.

This image processing method is advantageous in that it can realize anauto-focus function without modifying or adding the design of theoptical system such as lenses, and can improve the sensitivity to afocus error since the focus is adjusted using an image captured by theCCD.

Next, the infrared method applies the principles of triangulation tocalculate the subject distance. Specifically, the infrared methodirradiates an infrared ray from a video camera to a subject, detects anincident angle of return light reflected by the subject and returning tothe video camera, and then calculates the subject distance based on thedetected incident angle of the return light. The infrared method isadvantageous in that the subject distance can be sufficiently measured,even if the subject is dark, as long as the amount of return light fromthe subject exceeds a predetermined amount, since the infrared rayemitted from the video camera itself is irradiated to the subject.

Further, the phase difference detecting method provides two sets of lensgroups, each comprised of a small lens and a line sensor for detectingthe position of light, in a lens optical system of a camera, anddisposes the two sets of lens groups with their optical axes shiftedfrom each other to realize the aforementioned triangulation. This phasedifference detecting method is advantageous in that the capability ofdetecting a focusing state is constant irrespective of the subjectdistance.

The aforementioned image processing method, however, cannot detect afocusing stage unless the focus is moved to examine a change inevaluation value. Also, since the evaluation value varies in response toa small movement of a subject in the vertical direction with respect tothe optical axis, the focused position can be erroneously detected.Therefore, the image processing method experiences difficulties inmaking the focus smoothly follow movements of the subject in thedirection of the optical axis.

As a solution for the problems of the image processing method, theinfrared method and the phase difference detecting method have beenproposed. Since these methods can reveal a focusing state without movingthe focus, they need not move the focus to examine. the focusing state.In addition, even if a subject moves in the vertical direction withrespect to the optical axis, these methods will never erroneouslymeasure the subject distance. However, because of its limited ability ofmeasuring a distance of only about 10 m or less, the infrared method isnot suitable for a business-use video camera which may capture asubject, for example, at a distance exceeding 10 m with a small depth offield (a range centered on the subject in which the subject is infocus).

Also, in the infrared method, since an optical system for emitting aninfrared ray is generally disposed external to a video camera, theoptical axis of the video camera cannot be aligned with the optical axisof the infrared ray, causing a problem of discrepancy between an actualscreen range and a range viewed in a view finder, i.e., parallax.

FIG. 1 shows the principles as to how the parallax occurs. As shown inFIG. 1, a video camera 1 comprises a camera body 1A, and a camera lens1B, an infrared ray emitter 1C and a return light incident angledetector 1D mounted on the camera body 1A, and applies the principles oftriangulation to measure the subject distance.

Since the camera lens 1B is spaced from the infrared ray generator 1C bya predetermined distance, the optical axis A1 of an infrared ray is notcoaxial with the optical axis A2 of the camera. In the video camera 1,since the optical axis A1 of the infrared ray is offset from the opticalaxis A2 of the camera in this way, even if a subject B1 to be capturedis located on the optical axis A2 of the camera, the infrared ray may beirradiated to a subject B2 which is located on an axis offset from theoptical axis A2 of the camera, i.e., on the optical axis A1 of theinfrared ray.

In this event, the video camera 1 detects return light L1 from thesubject B2, which is not to be captured, to measure the distance to thesubject B2, and fails to measure the distance to the subject B1 to becaptured.

The phase difference detecting method, on the other hand, suffers from alower ability of measuring the subject distance as an iris of a cameralens is reduced. Specifically, since a video camera performs anauto-focus operation and an imaging operation simultaneously, the videocamera cannot open the iris in the auto-focus operation and reduces theiris during the imaging operation, as does a still camera whichseparately performs the auto-focus operation and the imaging operation.Thus, due to the requirement of adjusting the iris during the imagingoperation, the video camera cannot avoid a degradation in the ability ofmeasuring the distance to a subject, resulting from the reduced iris.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of this invention is to provide anauto-focus apparatus, a focus adjusting method, an image capturingapparatus and an image capturing method which are capable of accuratelyadjusting the focus on a subject to be captured.

The foregoing object and other objects of the invention have beenachieved by the provision of an auto-focus apparatus, a focus adjustingmethod, an image capturing apparatus and an image capturing method inwhich an irradiation wave is emitted from emitting means for irradiationto a subject while changing an incident angle of the irradiation wave,an incident angle of a reflected wave of the irradiation wave reflectedby the subject, incident on light receiving means positionedcorresponding to the emitting means, is detected, whether or not thesubject is a subject for which the focus is adjusted is determined basedon the emitting angle and the incident angle, and the focus is adjustedon the subject when determining that the subject is the subject forwhich the focus should be adjusted, thereby making it possible toaccurately adjust the focus on the subject for which the focus should beadjusted.

The nature, principle and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts aredesignated by like reference numerals or characters.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic diagram used for explaining the principles as tohow parallax occurs;

FIG. 2 is a schematic diagram used for explaining a video cameraaccording to the present invention;

FIG. 3 is a schematic diagram used for explaining how the distance to asubject is measured;

FIG. 4 is a block diagram illustrating the circuit configuration of thevideo camera;

FIG. 5 is a schematic diagram used for explaining how the distance to asubject is measured;

FIG. 6 is a schematic diagram showing the relationship between anemitting angle of an infrared ray and an incident angle of return light;

FIG. 7 is a schematic diagram showing the relationship between anemitting angle of an infrared ray and an incident angle of return light;and

FIG. 8 is a flow chart illustrating a focus adjustment processingprocedure.

DETAILED DESCRIPTION OF THE EMBODIMENT

Preferred embodiments of this invention will be described with referenceto the accompanying drawings:

FIG. 2 illustrates the configuration of a video camera, generallydesignated by reference numeral 10, which comprises a camera body 10A,and a camera lens 10B, an infrared ray emitter 10C as emitting means,and a return light incident angle detector 10D as incident lightdetecting means mounted at predetermined positions of the camera body10A. The video camera employs the infrared method as a focus detectingmethod, and applies the principles of triangulation to measure thedistance from the camera lens 10B to a subject, i.e., the subjectdistance.

In this embodiment, for measuring the subject distance, the infrared rayemitter 10C can vary (scan) the optical axis A10 of an infrared ray,i.e., the orientation of the infrared ray over an emitting angle in arange of θ1 to θu in the vertical direction.

In this event, an infrared ray scanning period is set, for example, to1/60 seconds, so that the infrared ray emitter 10C scans in a range ofthe emitting angle from θ1 to θu once for every 1/60 seconds. Also, theinfrared ray emitter 10C irradiates the infrared ray at a position onthe optical axis A11 of the camera spaced by a distance 0.8 m from thecamera lens 10B when the infrared ray is emitted at angle θ1, andirradiates the infrared ray at a position on the optical axis A11 of thecamera spaced by a distance 30 m from the camera lens 10B when theinfrared ray is emitted at angle θu. In this way, the infrared rayemitter 10C can irradiate the infrared ray to a subject which is locatedon the optical axis A11 of the camera and distanced from the camera lens10B in a range of 0.8 to 30 m.

FIG. 3 shows how to measure the subject distance when a subject B10 islocated on the optical axis A11 of the camera. In this event, theinfrared ray emitter 10C irradiates an infrared ray L10 to the subjectB10 at an emitting angle θu. The infrared ray L10 is reflected by thesubject B10, and return light L11 from the subject B10 is incident onthe return light incident angle detector 10D at an incident angle θub.

When the subject B10 is located on the optical axis A11 of the camera asdescribed above, the subject distance is uniquely determined when theincident angle θub of the return light is determined. Therefore, thereturn light incident angle detector 10D measures the incident angle θubof the return light L11 to calculate the subject distance Lu based onthe incident angle θub and the distance between the camera lens 10B andthe return light incident angle detector 10D. Then, the video camera 10adjusts the focus in accordance with the thus calculated subjectdistance Lu.

Here, the circuit configuration of the video camera 10 is illustrated inFIG. 4. A Central Processing Unit (CPU) 15 is mounted in the camera body10A to control the general operation of the video camera 10. The CPU 15periodically (for example, every 30 msec) checks whether a push switch16, disposed external to the video camera 10, is pressed, and generatesinstruction data S1 for emitting an infrared ray when it detects thatthe push switch 16 is pressed.

The CPU 15 sends the instruction data S1 to a digital-to-analog (DA)converter circuit 17 which converts the instruction data S1 to an analoginstruction signal S2 which is then sent to an Laser Diode (LD) drivingcircuit 18 in the infrared ray emitter 10C. The LD driving circuit 18,in response to the instruction signal S2, drives an LD 19 as a lightemitting element, and applies the LD 19 with a current. Then, the LD 19emits laser light L15 in accordance with the applied current.

The laser light L15 emitted from the LD 19 is transformed to a divertingbeam L16 having a diverting angle proximal to a parallel beam by a lens20, reflected by a mirror 21 comprised of a flat mirror, and irradiatedto the space as an infrared ray L17.

In this embodiment, the infrared ray emitter 10C employs, as a lightemitting element, the LD 19, referred to as an eye safe laser diode,which is highly safe to eyes and oscillates in a 1400 nm 0 band ofwavelength, and irradiates the laser light L15 with large powerexceeding 200 mW. The video camera 10, therefore, ensures the safety tothe eyes of the user, as well as can extend a measurable distance to 30m, i.e., approximately three times the conventional light emitting diodewhich is measurable up to approximately 10 m with power of 20 mW, by wayof example.

The CPU 15, upon detection of the pressed push switch 16, also generatesdriving data S5 for driving a motor 22 coupled to the mirror 21 in theinfrared ray emitter 10C. The CPU 15 sends the driving data S5 to adigital-to-analog (DA) converter circuit 25 which converts the drivingdata S5 to an analog driving signal S6 which is then sent to a motordriving circuit 26 in the infrared ray emitter 10C. The motor drivingcircuit 26 drives the motor 22 based on the driving signal S6 to changethe inclination of the mirror 21, thereby allowing an infrared ray L17to be irradiated to a subject which is located on the optical axis A11of the camera (FIG. 2) at a distance of 0.8 to 30 m from the camera lens10B.

An inclination sensor 27 is provided near the mirror 21, such that aninclination sensor detector circuit 28 detects the inclination of themirror 21 through the inclination sensor 27 to generate a mirrorinclination signal S8. Then, the inclination sensor detector circuit 28sends the mirror inclination signal S8 to an analog-to-digital (AD)converter circuit 29 which converts the mirror inclination signal S8 todigital mirror inclination data S9 which is sent to the CPU 15.Therefore, the CPU 15 can know the inclination of the mirror 21 based onthe mirror inclination data S9. In this way, the CUP 15 measures theorientation of the infrared ray L17 emitted from the infrared rayemitter 10C while changing the orientation of the infrared ray L17.

Also, the CPU 15 controls the power of the emitted infrared ray L17 inaccordance with a change in the orientation of the infrared ray L17,i.e., a change in the distance from the camera lens 10B to a position tobe measured to reduce the power consumption and extend the lifetime ofthe LD 19. Specifically, for example, the CPU 15 sets the emission powerat 200 mW when the infrared ray L17 is irradiated at a distance of 30 mfrom the camera lens 10B, while sets the emission power at 2 mW when theinfrared ray L17 is irradiated at a distance of 3 m from the camera lens10B, thereby controlling the return light incident on the return lightincident angle detector 10D to a constant amount.

The return light L20 from a subject is incident on a lens 35 in thereturn light incident angle detector 10D, and is converged by the lens35 on a light receiving surface of a Position Sensitive Diode (PSD) 36as position detecting element. The PSD 36 generates a current inaccordance with the centroid of the magnitude of the return light L20converged on the light receiving surface, and sends the current to thereturn light incident angle detector 37.

The PSD 36 has the light receiving surface in alignment with the focalplane of the lens 35, so that the incident angle of the return light L20is uniquely determined when the position of the return light L20converged on the light receiving surface of the PSD 36 is determined.Therefore, the return light incident angle detector circuit 37, servingas detecting means, detects the incident angle of the return light L20based on the current supplied from the PSD 36. Then, the return lightincident angle detector circuit 37 sends the detected incident angle ofthe return light L20 to an analog-to-digital (AD) converter circuit 38of the camera body 10A as a return light incident angle signal S12. TheAD converter circuit 38 converts the return light incident angle signalS12 to digital return light incident angle data S13 which is sent to theCPU 15.

The CPU 15 calculates the subject distance based on the emitting angleof the infrared ray L17 derived from the mirror inclination data S9 andthe incident angle of the incident angle L20 derived from the returnlight incident angle data S13, and sends the subject distance to thecamera lens 10B as subject distance data S15 to adjust the focus suchthat the focus of the camera lens 10B is coincident with the subjectdistance. For reference, the CPU 15 sends the subject distance data S15to the camera lens 10B every 1/60 seconds to make the focus smoothlyfollow movements of the subject.

Here, FIG. 5 shows a situation in which a subject B10 to be imaged islocated on the optical axis A11 of the camera, and a subject B11 not tobe imaged is located at a position apart from the optical axis A11 ofthe camera, wherein an infrared ray L20 is irradiated to the subject B11not to be imaged while the infrared ray L20 is being scanned.

In this situation, return light L21 reflected by the subject B11 isincident on the return light incident angle detector 10D at an incidentangle θxb. In this event, a conventional video camera calculates asubject distance based only on the incident angle θxb of the returnlight L21. As a result, the video camera disadvantageously determinesthat the subject exists at a position of a point Pb on the optical axisA11 of the camera, and focuses at the position of the point Pb on theoptical axis A11 of the camera.

To eliminate this disadvantage, the CPU 15 (FIG. 4) of the video camera10 previously holds in an internal memory incident/emitting relationdata (FIG. 6) indicative of the relationship between the emitting angleof the infrared ray and the incident angle of return light when asubject exists on the optical axis A11 of the camera, and determineswhether or not the detected emitting angle of the infrared ray andincident angle of the return light match the incident/emitting relationdata.

As a result, when determining that the detected emitting angle of theinfrared ray and incident angle of the return light match theincident/emitting relation data, the CPU 15 determines that the subjectexists on the optical axis A11 of the camera, and calculates thedistance to the subject. On the other hand, when determining that thedetected emitting angle of the infrared ray and incident angle of thereturn light do not match the incident/emitting relation data, the CPU15 determines that the subject does not exist on the optical axis A11 ofthe camera, and that the subject is not to be imaged.

For example, in FIG. 5, when the video camera 10 changes the emittingangle of the infrared ray L20 from θ1 to θ2, the infrared ray L20 isfirst irradiated to the subject B11, and next to the subject B10. Inthis event, the return light incident angle detector 10D receives returnlight L21 from the subject B11 to detect an incident angle θBb, and nextreceives return light from the subject B10 to detect-an incident angleθAb, as shown in FIG. 7.

Thus, the CPU 15 (FIG. 4) is provided with position data PB (θB, θBb) ofthe subject B11 and position data PA (θA, θAb) of the subject B10, anddetermines based on the aforementioned incident/emitting relation datathat only the subject B10 is located on the optical axis A11 of thecamera. Eventually, the CPU 15 determines the subject B10 as a subjectto be imaged, and calculates the distance to the subject B10 to adjustthe focus.

As described above, in FIG. 8, the CPU 15, when entering a focusadjustment processing procedure RT1, proceeds to step SP1 to initiateevery 1/60 seconds, and determines whether or not the push switch 16 ispressed at subsequent step SP2.

When an affirmative result is returned at step SP2, this means that thepush switch 16 is pressed by the user, in which case, the CPU 15proceeds to step SP3, where the CPU 15 forces the LD 19 to emit laserlight L15. Conversely, when a negative result is returned at step SP12,this means that the push switch 16 is not pressed by the user, in whichcase, the CPU 15 proceeds to step SP4 to terminate the processingprocedure.

Then, the CPU 15 proceeds to step SP4, where the CPU 15 drives the motor22 through the motor driving circuit 26 to change the inclination of themirror 21 to change the orientation of the infrared ray, andperiodically samples the inclination of the mirror 21 derived from theinfrared ray emitter 10C and the incident angle of return light derivedfrom the return light incident angle detector 10D to store in theinternal memory sampling data comprised of the emitting angle of theinfrared ray indicated by the inclination of the mirror 21 and theincident angle of the return light thus derived.

Then, the CPU 15 turns off the LD 19 at step SP5, and proceeds to stepSP6, where the CPU 15 acts as determining means to search the samplingdata for one indicative of return light from a subject located on theoptical axis A11 of the camera, and to calculate the subject distancebased on the incident angle of the found return light.

Next, the CPU 15 acts as adjusting means at step SP7, where the CPU 15notifies the camera lens 10B of the calculated subject distance toadjust the focus such that the focus of the camera lens 10B matches thesubject distance. Subsequently, the CPU 15 proceeds to step SP4 toterminate the processing procedure.

In the foregoing configuration, the infrared ray emitter 10C changes theemitting angle of the infrared ray under the control of the CPU 15 toemit the infrared ray, detects the emitting angle, and notifies the CPU15 of the detected emitting angle. The infrared ray emitted from theinfrared ray emitter 10C is reflected by a subject and incident on thereturn light incident angle detector 10D. The return light incidentangle detector 10D detects the incident angle of the return light fromthe subject, and notifies the CPU 15 of the detected incident angle.

The CPU 15 determines based on the emitting angle of the infrared andthe incident angle of the return light, detected when the infrared rayis irradiated to the subject, whether or not the subject exists on theoptical axis A11 of the camera, and calculates the subject distancebased on the incident angle of the return light from the subject whendetermining that the subject exists on the optical axis A11 of thecamera. Then, the CPU 15 adjust the focus of the camera lens 10B usingthe calculated subject distance.

Consequently, the video camera 10 prevents the calculation of thesubject distance based on the incident angle of return light reflectedby and returned from a subject which does not exist on the optical axisA11 of the camera, i.e., a subject not to be imaged.

According to the foregoing configuration, the infrared ray is emitted asthe emitting angle thereof is changed, and it is determined based on theemitting angle of an infrared ray and an incident light of its returnlight, which are detected when the infrared ray is irradiated to asubject, whether or not the subject exists on the optical axis of thecamera before the subject distance is calculated, thereby making itpossible to accurately calculate the subject distance and accomplishmore accurate focus adjustments as compared with the prior art.

While the foregoing embodiment has been described in connection with aflat mirror which is employed as the mirror 21 for changing the emittingangle of the infrared ray, the present invention is not limited to thisparticular mirror, but can employ a mirror in any of other variousshapes, such as a polygon mirror, by way of example.

Also, while the foregoing embodiment has been described in connectionwith the PSD 36 employed as the position detecting element, the presentinvention is not limited to this particular element, but can employ anyof other various position detecting elements such as a bisect pinphotodiode, by way of example.

Further, while the foregoing embodiment has been described for aspecific configuration in which the infrared ray is emitted as itsorientation is changed, the present invention is not limited to thisconfiguration. Alternatively, a plurality of infrared ray emitters foremitting infrared rays in different orientations from one another can beprovided such that desired one is selected and lit from the plurality ofinfrared ray emitters as required.

Further, while the foregoing embodiment has been described for aspecific configuration in which an infrared ray is irradiated to asubject to calculate the subject distance, the present invention is notlimited to this configuration. Alternatively, any of other variousirradiation waves such as ultrasonic waves, by way of example, can beirradiated to a subject to calculate the subject distance.

Further, while the foregoing embodiment has been described in connectionwith the video camera 10 to which the present invention is applied, thepresent invention is not limited to the video camera but can be appliedwidely to a variety of other auto-focus apparatus which contain anauto-focus function such as a still camera for photographing a stillimage, by way of example.

As described above, according to the present invention, the auto-focusapparatus irradiates an irradiation wave from emitting means to asubject while changing an emitting angle of the irradiation wave,detects an incident angle of a reflected wave of the irradiation wavereflected by the subject, incident on light receiving means positionedcorresponding to the emitting means, determines based on the emittingangle and the incident angle whether or not the subject is a subject forwhich the focus should be adjusted, and adjusts the focus on the subjectwhen determining that the subject is the subject for which the focusshould be adjusted, thereby making it possible to accurately adjust thefocus on the subject for which the focus should be adjusted.

While there has been described in connection with the preferredembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be aimed, therefore, tocover in the appended claims all such changes and modifications as fallwithin the true spirit and scope of the invention.

1. An image capturing apparatus comprising: generating means forgenerating an instruction to emit irradiation as a function of an input;emitting means for emitting an irradiation wave for irradiation to asubject while changing an emitting angle of said irradiation wave;detecting means for detecting an incident angle of a reflected wave ofsaid irradiation wave reflected by said subject, incident on lightreceiving means positioned corresponding to said emitting means;determining means for determining based on said emitting angle and saidincident angle whether or not said subject is a subject for which thefocus should be adjusted; and adjusting means for adjusting the focus onsaid subject when determining that said subject is the subject for whichthe focus should be adjusted, wherein said determining means comprises astorage means for storing sampling data of said emitting angle and saidincident angle, and wherein said determining means comprises a storagemeans for storing correspondence data of said emitting angle and saidcorresponding incident angle.